Multi-mode mobile stations are mobile stations (MS) that have the capability to access different types of radio access systems. Existing multi-mode mobile stations include mobile stations with a combination of Global System for Mobile Communications/General Packet Radio Services (GSM/GPRS) and Code Division Multiple Access (CDMA) capabilities, and mobile stations with a combination of GSM/GPRS/Universal Mobile Telecommunications System (UMTS) and CDMA capabilities, and combinations that include wireless large area network (WLAN) capabilities.
When a multi-mode mobile station enters a new network and when the multi-mode mobile station changes to an alternate radio access technology (RAT) within a network, the number of concurrent data sessions, or more specifically packet data protocol (PDP) contexts in 3GPP networks such as GSM/GPRS and UMTS, that are supported by the new network or alternate RAT may be different than a number supported by a previous network that the multi-mode mobile station came from or a previous RAT the multi-mode mobile station was using before changing to the alternate RAT. When the multi-mode mobile station enters a new network or changes to an alternate RAT that has only a single PDP context, this can be problematic if the multi-mode mobile station has an always-on service/application. The always-on service application will utilize the single PDP context available to the multi-mode mobile station and other services/applications will have no access to the network, as the network does not allow any subsequent concurrent PDP context activations on alternate subscribed access point name (APN) or data service. It may be possible for the multi-mode mobile station to occasionally disconnect the PDP context of the always-on application to allow other services/applications access to the network, but then the always-on application is not technically always-on, which may result in delays in the always-on service/application that a user of the multi-mode mobile station cannot tolerate. More generally, a problem can also arise when entering a new network or an alternate RAT in which the number of PDP contexts is less than the number of PDP contexts supported in a previous network or RAT.
GPRS supports multiple PDP contexts between multi-mode mobile stations and a GPRS enabled network. In some situations, Universal Mobile Telecommunications System (UMTS) supports only a single packet data protocol (PDP) context between a multi-mode mobile station and a UTMS enabled network. A multi-mode mobile station can support multiple PDP contexts for enabling multiple services/applications to occur simultaneously between the multi-mode mobile station and the network. Some examples of services/applications include wireless application protocol (WAP), mobile message service (MMS), push e-mail, WAN data modem and SIP/IMS (Session Initiation Protocol/IP Multimedia Subsystem) services (e.g. Push to talk over cellular).
Global System for Mobile Communications (GPRS) is an example of a second generation (2G) RAT, while UMTS is an example of a third generation (3G) RAT.